U.S. Pat. No. 8,434,396 (incorporated by reference), which is assigned to the assignee of the present application, discloses a hexagonal-shaped ceramic tile design (hereafter Verco tile).
U.S. Pat. No. 8,434,396 also discloses an armor system comprised of an imbricated pattern of Verco tiles that are wrapped with a ballistic fabric for use in the construction of a flexible/conformable personal armor system.
U.S. Pat. No. 8,434,396 discloses a method of wrapping the individual tiles with, for example, a glass fiber fabric, and encasing the imbricated pattern of the wrapped tiles in between ballistic fabric layers.
Ceramic tiles made from hard ceramics such as aluminum oxide (Al2O3), silicon carbide (SiC), and boron carbide (B4C) have very effective strike faces for defeating projectiles such as armor piercing rifle rounds and shrapnel. Unlike ductile metals which flow out of the way of a penetrating projectile, the aforementioned brittle (no plastic flow) and very hard ceramics imbue a dwell period during early projectile/ceramic surface interaction, during which the projectile collapses upon itself and mushrooms laterally outward. During this period, a compressive wave extends to the back face of the ceramic tile and returns as a tensile wave to pulverize the ceramic tile. The projectile is then partially ablated by the loose ceramic as it penetrates through. The remaining kinetic energy of the projectile, or its fragments, is captured by a backing, typically made up of layers of pressed high molecular weight polyethylene fibers.
Personal armor plates, e.g. ESAPI plates (enhanced small arms protective insert, a U.S. military specification), are known to be effective against specified ballistic threats for the first impact, but multiple shots to the same plate are challenged by the propensity for the fracture cracks to extend well away from previous points of impact. Additional problems with such monolithic torso plates are their tendency to fracture with rough handling. Monolithic torso plates also impose a turtle-like rigid discomfort and immobility to the wearer.
A flexible armor system, by contrast, facilitates greater body-conformability and body movement. A flexible armor system also exhibits improved multi-hit capabilities since only the impacted tile is damaged. That is, the tiles surrounding the tile that has been hit may be left in pristine condition, with uncompromised ability to defeat the next projectile.
In an imbricated armor system, when a bullet hits a ceramic strike face near its edge, ballistic stopping performance decreases because of an increasing propensity for the ceramic to chip out of the way of the projectile. An imbricated tile flexible system has an array of near-edge regions that are not present in a monolithic plate. The design of an imbricated system typically compensates for the adverse effects of the near-edge regions by partially overlapping the ceramic tiles, so that the bullet interacts with more than one ceramic tile in the near-edge regions.
Wrapping the ceramic tiles with a strong fabric to reduce the probability of the ceramic chipping out of the way of the projectile is an important contributor to reducing the adverse edge effects created by the array of near edge regions in an imbricated armor system.
An objective of the disclosed method is a new method of wrapping ceramic tiles suitable for use in a flexible armor system, and optimizing the cohesion between the ceramic and the wrap.
Another objective is a wrapped ceramic tile suited for construction of a flexible armor system.
A further objective is a flexible armor system with wrapped ceramic tiles.
A method of making an armor component according to the present invention includes wrapping a ceramic tile with a plurality of wrappers impregnated with a curable polymer to obtain a wrapped tile and isostatic pressing the wrapped tile to integrate the wrappers and the tile while curing the polymer.
The isostatic pressing may be carried out in a chamber of an isostatic press. The method may further include initially pressurizing the chamber to a first pressure above atmospheric pressure while at a first, ambient temperature and thereafter further increasing pressure to a second higher pressure, while increasing temperature to a second, higher temperature to cure the polymer, and holding temperature of the chamber for a first period of time at the second temperature to cure the polymer. Thereafter, the chamber may be cooled from the second, higher temperature to a lower temperature above ambient temperature without venting the chamber to maintain the pressure inside the chamber, and then venting the chamber while maintaining the temperature of the chamber above ambient. Alternatively, the chamber may be vented to atmospheric pressure while maintaining the second, higher temperature for a second period of time.
Prior to isostatic pressing, the wrapped tile may be sandwiched between release fabrics to obtain a sandwiched and wrapped tile. The sandwiched and wrapped tile may be placed in a vacuum bag followed by evacuating the vacuum bag, thereby squeezing the wrappers into tighter contact with the tile. The bag is then sealed to obtain an air-tight enclosure.
The tile may include rounded corners, and the plurality of wrappers include at least a first wrapper and at least a second wrapper, each wrapper having a central portion and a plurality of leaves of varying lengths surrounding and extending from the central portion, at least some of the leaves being shorter than other leaves. The central portion of the first wrapper may be placed over the first side of the tile with the shorter leaves of the first wrapper being closer to the rounded corners of the tile, and the leaves of the first wrapper may be folded over to the second side of the tile. The central portion of the second wrapper may be placed over the second side of the tile with the shorter leaves of the second wrapper being closer to the rounded corners of the tile, and the leaves of the second wrapper may be folded over to the first side of the tile and the central portion of the first wrapper.
The second side may be the strike face of the tile.
The plurality of wrappers may include at least a third wrapper having a central portion and a plurality of leaves of varying lengths surrounding and extending from the central portion, at least some of the leaves being shorter than other leaves of the third wrapper. The central portion of the third wrapper may be placed over the first side of the tile with the shorter leaves of the third wrapper being closer to the rounded corners of the tile, and the leaves of the third wrapper may be folded over to the second side of the tile.
According to one aspect of the present invention, the leaves of the first wrapper and the leaves of the third wrapper are off-set by reversing the contacting face of the wrapper.
The tile may be symmetric about a symmetry line and the shape and seam positions of the leaves of the wrappers are asymmetric about the symmetry line.
The wrappers may be star-shaped with leaves that terminate at respective points. The polymer may comprise an epoxy and the wrappers may comprise carbon fibers.
A method according to the present invention can be used to fabricate an armor component that includes a tile wrapped with a plurality of polymer impregnated wrappers, in which the polymer penetrates microscopic surface cavities of the tile to mechanically bond the wrappers to the ceramic tile.
Preferably the tile comprises a ballistic material such as boron carbide, the polymer comprises cured epoxy and the wrapper comprises carbon fibers. Other ballistic materials such as silicon carbide can also be used without deviating from the present invention.
In the preferred embodiment, the tile includes a plurality of rounded corners. The plurality of wrappers include at least a first wrapper and at least a second wrapper, each wrapper having a central portion and a plurality of leaves of varying lengths surrounding and extending from the central portion, at least some of the leaves being shorter than other leaves. The central portion of the first wrapper resides over the first side of the tile with the shorter leaves of the first wrapper being closer to the rounded corners of the tile and the leaves of the first wrapper are folded over to the second side of the tile. The central portion of the second wrapper resides over the second side of the tile with the shorter leaves of the second wrapper being closer to the rounded corners of the tile, and the leaves of the second wrapper are folded over to the first side of the tile and the central portion of the first wrapper.
The plurality of wrappers may include at least a third wrapper having a central portion and a plurality of leaves of varying lengths surrounding and extending from the central portion, at least some of the leaves being shorter than other leaves of the third wrapper. The central portion of the third wrapper resides over the first side of the tile with the shorter leaves of the third wrapper being closer to the rounded corners of the tile, and the leaves of the third wrapper are folded over the second side of the tile.
An armor component made with a method according to the present invention may be used in an armor. Thus, an armor can be made by imbricating a plurality of armor components into an imbricated pattern.